1. Field of the Invention
The present invention relates to a system and method for mixing gaseous fuel with air, and more particularly, to a system and method for mixing gaseous fuel with air in a dual fuel system of an internal combustion engine.
2. Prior Art
Various types of carburetors have been developed for internal combustion engines to solve the basic problem of mixing liquid gasoline fuel with air to provide a combustible fuel/air mixture. Problems inherent in the carburetion of liquid fuels have led many to explore gaseous fuels, such as propane, as an alternative to conventional gasoline or diesel fuels. Thus, many different carburetors or mixers have been developed for gaseous fuel systems.
Much development has occurred particularly in the area of "conversion kits" for gaseous fuel mixers which are adapted for installation in the gasoline fuel carburetion system of an ordinary internal combustion engine. These so-called conversion kits are intended to provide a dual fuel system which will permit operation of the engine on liquid fuel alone, gaseous fuel alone, and in some systems, combinations of the two fuels.
The prior art gaseous fuel mixers can be generally classified ito three categories based on the type of installation within the combustion engine: (1) mixers which are installed between the intake manifold and the carburetor; (2) mixers which are installed directly inside of or around the carburetor; and (3) mixers which are installed within or adjacent the air filter housing so as to release gaseous fuel inside the air filter.
Generally speaking, each of these types of gaseous fuel mixers is difficult to install. The desired connections are often congested with throttle linkage, choke linkage, vacuum hoses, fuel lines, valve lines, and the like. Moreover, typically the prior art fuel mixers require complicated adjustments in order to adapt them to the characteristics of a particular combustion engine.
Another common installation problem is that portions of the original engine equipment must be replaced or modified to accommodate installation of the prior art type mixers. As a result, time-consuming modifications must be made to the engine. For example, often it ocurs that a gaseous fuel mixer cannot be used with the existing air intake system of the combustion engine. This necessitates providing the mixer with a vacuum-creating device or pressurizing the gaseous fuel before injection into the air flow to obtain an adequate fuel/air mixture. Also, prior art fuel mixers of the third type, those releasing gaseous fuel inside the air filter, are commonly connected to a gaseous fuel line through the top of the air filter housing. Such fuel line connections frequently require modification of the car hood to accommodate the gaseous fuel lines.
Another significant problem experienced with the prior art type fuel mixers is that proper mixing of the gaseous fuel with the air flowing into the combustion engine is difficult to achieve. The basic problem is how to combine the fuel and air particles into a homogeneous mixture. An important factor in achieving a homogeneous mixture of fuel and air is the path of the air flow in relation to the entry of the gaseous fuel into the air flow. In nearly every internal combustion engine, the air flow is irregular between the air filter and the engine cylinders, and since most prior art fuel mixers use the existing air flow system of the internal combustion engine, some of the engine cylinders receive a richer gaseous fuel/air mixture than other cylinders. Thus, to compensate, the rate of gaseous fuel injection into the air flow is increased so that combustion will still occur within the cylinders receiving the leanest air/fuel mixture. By adjusting the rate of fuel flow to provide the leanest cylinder with an optimum air/fuel mixture, the other cylinders consequently receive a richer air/fuel mixture than is necessary for combustion, resulting in wasted fuel and poor engine efficiency. This problem is compounded by the fact that in many cases, the very installation of the prior art type gaseous fuel mixers tends to render the incoming air flow more irregular.
A further problem of nearly every prior art type mixer is that additional gaseous fuel is wasted during acceleration of the engine due to the effect of the engine vacuum during the air response delay between the engine cylinders and the air inlet of the air intake system. Typically, when a driver depresses the accelerator pedal of his vehicle to accelerate the engine, a series of butterfly valves in the carburetor are opened to allow more fuel/air mixture to enter the cylinders, thus increasing the power output of the engine. Upon opening these valves, the air flow within and immediately around the carburetor is suddenly exposed to a vacuum created by the engine pistons. The influence of the vacuum is transferred back through the engine's air flow system until satisfied by the incoming air that is drawn through the air intake. With the prior art type mixers, this momentary vacuum imposed on the prior art type mixers causes additional fuel to exit the fuel mixing device and mix with the air flow, thus yielding a gaseous fuel/air mixture which is considerably richer than the optimum mixture needed for combustion. As a result, the excess gaseous fuel injected into the air flow is wasted. And when the air filter of the internal combustion engine is dirty or becomes wet, the air flow is further impeded and even more gaseous fuel is wasted due to a longer air response delay during acceleration.
In view of the foregoing, what is needed in the art is a gaseous fuel mixer for a dual fuel system of an internal combustion engine that overcomes these and other problems of the prior art, and yet is economical and simple to construct and install.